Semiconductor light receiving element and semiconductor relay

ABSTRACT

A semiconductor relay includes: a substrate; a semiconductor layer of a direct transition type which is on the substrate and which has semi-insulating properties; a p-type semiconductor layer on at least part of the semiconductor layer; a first electrode; and a second electrode. The first electrode is electrically connected to the semiconductor layer and in contact with the p-type semiconductor layer. The second electrode is spaced apart from the first electrode and at least partially in contact with one of the semiconductor layer and the substrate, and the first electrode includes a first opening part.

TECHNICAL FIELD

The present disclosure relates to a semiconductor light receivingelement capable of performing switching control as a result of a changein the inner resistance after light absorption and to a semiconductorrelay including same.

BACKGROUND ART

A relay is a component which switches between an ON state and an OFFstate of an electric circuit in accordance with a signal received froman outside. The relay can be largely classified into: a mechanical relaywhich mechanically opens and closes a node of the electric circuit; anda semiconductor relay which uses a semiconductor. The relay is widelyused for, for example, consumer devices such as home devices, industrialdevices, and medical devices.

In particular, the semiconductor relay has excellent properties such ashigh reliability, a long life, a compact size, a fast operation speed,and small operation noise, and thus the semiconductor relay is utilizedin, for example, precision devices and compact devices. For example,Patent Literature (PTL) 1 discloses a semiconductor relay including astructure which can be fabricated through an easy process.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No.2013-191705

SUMMARY OF THE INVENTION Technical Problem

The present disclosure provides a semiconductor light receiving elementcapable of efficiently irradiating light to a semiconductor layer.

Solutions to Problem

A semiconductor light receiving element according to one aspect of thepresent disclosure includes: a substrate; a semiconductor layer of adirect transition type which is on the substrate and which hassemi-insulating properties; a p-type semiconductor layer on at leastpart of the semiconductor layer; a first electrode electricallyconnected to the semiconductor layer and in contact with the p-typesemiconductor layer; and a second electrode spaced apart from the firstelectrode and at least partially in contact with one of thesemiconductor layer and the substrate, and the first electrode includesa first opening part.

Advantageous Effect of Invention

With the present disclosure, a semiconductor light receiving element isrealized which can efficiently irradiate light to a semiconductor layer.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of a semiconductor relay accordingto a comparative example.

FIG. 2 is a schematic sectional view of a semiconductor relay accordingto Embodiment 1.

FIG. 3 is a top view of a semiconductor light receiving elementaccording to Embodiment 1.

FIG. 4 is a schematic sectional view of a semiconductor relay accordingto Variation 1.

FIG. 5 is a top view of a semiconductor light receiving elementaccording to Variation 1.

FIG. 6 is a schematic sectional view of a semiconductor relay accordingto Variation 2.

FIG. 7 is a top view of a semiconductor light receiving elementaccording to Variation 2.

FIG. 8 is a schematic sectional view of a semiconductor relay accordingto Variation 3.

FIG. 9 is a top view of a semiconductor light receiving elementaccording to Variation 3.

FIG. 10 is a top view of a semiconductor light receiving elementaccording to Variation 4.

FIG. 11 is a schematic sectional view of the semiconductor lightreceiving element according to Variation 4, taken along line XI-XI ofFIG. 10.

FIG. 12 is a schematic sectional view of the semiconductor lightreceiving element according to Variation 4, taken along line XII-XII ofFIG. 10.

FIG. 13 is a top view of a semiconductor light receiving elementaccording to Variation 5.

FIG. 14 is a first top view of a semiconductor light receiving elementaccording to Variation 6.

FIG. 15 is a second top view of the semiconductor light receivingelement according to Variation 6.

FIG. 16 is a third top view of the semiconductor light receiving elementaccording to Variation 6.

FIG. 17 is a plan view of a semiconductor light receiving element forexplaining a first modified example of a first opening part.

FIG. 18 is a plan view of a semiconductor light receiving element forexplaining a second modified example of the first opening part.

FIG. 19 is a schematic sectional view of a semiconductor light receivingelement realized as a horizontal device.

FIG. 20 is a schematic sectional view of another semiconductor lightreceiving element realized as a horizontal device.

FIG. 21 is a first schematic sectional view of a semiconductor relayhaving different impurity concentrations in a stacking direction.

FIG. 22 is a second schematic sectional view of the semiconductor relayhaving the different impurity concentrations in the stacking direction.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

(Knowledge as Basis of the Present Disclosure)

Hereinafter, the knowledge as the basis of the present disclosure willbe described with reference to a structure of a semiconductor relayaccording to a comparative example. FIG. 1 is a schematic sectional viewof the semiconductor relay according to the comparative example.

Semiconductor relay 10 z according to the comparative exampleillustrated in FIG. 1 is a semiconductor relay which uses asemiconductor of a direct transition type having semi-insulatingproperties. Semiconductor relay 10 z includes light emitting element 20and semiconductor light receiving element 30 z which also serves as acontrol circuit. Semiconductor light receiving element 30 z includes:substrate 31, semiconductor layer 32 of a direct transition type whichis on substrate 31 and which has semi-insulating properties; firstelectrode 33, second electrode 34, p-type semiconductor layer 36, outputterminal 51, and output terminal 52.

As a result of voltage application between input terminal 41 and inputterminal 42 of light emitting element 20, light emitting element 20emits light. Upon irradiation of semiconductor layer 32 of semiconductorlight receiving element 30 z having light with energy more than or equalto the band gap of semiconductor layer 32 from light emitting element20, the conductivity of a region (in other words, a light receivingregion) of semiconductor layer 32 irradiated with the aforementionedlight changes. More specifically, the resistance of the light receivingregion decreases. Consequently, a region of semiconductor layer 32between output terminal 51 and output terminal 52 is conducted, wherebya current flows between output terminal 51 and output terminal 52.

Downsizing and cost reduction are more easily achieved in semiconductorrelay 10 z which uses semiconductor layer 32 as described above than intypical semiconductor relays. In the typical semiconductor relays, thedirect driving of a metal-oxide-semiconductor field-effect transistor(MOSFET) by light cannot be performed, which therefore requires anelement for converting light of, for example, a solar battery into avoltage. On the contrary, semiconductor light receiving element 30 zalone can play a role of the solar battery and the MOSFET insemiconductor relay 10 z. Thus, the number of components formingsemiconductor relay 10 z can be reduced.

Moreover, the typical semiconductor relays require three types ofoperation for switching, which therefore makes it difficult to performhigh-speed operation. More specifically, the three types of operationsinclude: operation of applying a voltage to a light-emitting diode tocause emission; operation of converting light from the light-emittingdiode into a voltage by the solar battery; and operation of electricallycharging the gate of the MOSFET by a current outputted from the solarbattery. The operation of electrically charging the gate of the MOSFETby the current outputted from the solar battery in particular is timeconsuming, which therefore makes it difficult for the typicalsemiconductor relays to perform high-speed switching of ns to μs order.

On the contrary, the operation of converting the light from thelight-emitting diode into a voltage by the solar battery (that is, relayoperation performed via the solar battery) is not required insemiconductor relay 10 z. Thus, it is possible to achieve an increase inthe speed of the switching operation.

For semiconductor layer 32 of semiconductor light receiving element 30z, a semiconductor material is used which has a wide band gap of adirect transition type containing InAlGaN. Such a semiconductor materialhas higher dielectric breakdown electric field strength than Si which isused in the typical semiconductor relays. Thus, forming semiconductorlayer 32 with a semiconductor material having a wide band gap of adirect transition type makes it possible to increase the pressureresistance of semiconductor relay 10 z. Moreover, for the purpose ofincreasing the pressure resistance and reducing the leak current, p-typesemiconductor layer 36 is under first electrode 33 in semiconductorlight receiving element 30 z. Hereinafter, the effects provided byp-type semiconductor layer 36 will be described.

When light emitting element 20 lights off, a higher voltage is appliedto output terminal 52 than to output terminal 51. At this point, areverse voltage is applied to a pn-junction of p-type semiconductorlayer 36 and semiconductor layer 32 and a depletion layer extends fromp-type semiconductor layer 36. Thus, it is possible to improve thedielectric voltage of semiconductor light receiving element 30 z. It isalso possible to reduce the leak current.

On the other hand, electrode 33 z is formed of a material which forms anohmic junction with semiconductor layer 32 when light emitting element20 lights up. Thus, absorbing light from light emitting element 20 toreduce the resistance of semiconductor layer 32 causes a flow of an ONcurrent between the output terminals through a portion of contactbetween semiconductor layer 32 and electrode 33 z.

Semiconductor relay 10 z is required to suppress the leak current at OFFtime when light emitting element 20 lights off and also to provide agreat ON current when the light emitting element lights up.

It has been found through the review by the inventors that semiconductorrelay 10 z described above can perform light uptake only from an outercircumferential part of electrode 33 z. Thus, there has arisen a problemthat the resistance of a portion of semiconductor layer 32 located underelectrode 33 z cannot be effectively reduced, which makes it difficultto provide a great current at ON time.

As one means for solving this problem, it is possible to use, aselectrode 33 z, a transparent electrode material for the light emittedfrom light emitting element 20. However, as a result of review of theelectrode material, it has been found that it is difficult to form afavorable ohmic junction with semiconductor layer 32 while providinghigh transmittance for the light (with a wavelength of, for example, 365nm) emitted from light emitting element 20.

Then the inventors have found a configuration such that whilesuppressing the leak current when light emitting element 20 lights off,the ON current when light emitting element 20 lights up is increased(that is, providing a great current is achieved).

A semiconductor light receiving element according to one mode of thepresent disclosure includes: a substrate; a semiconductor layer of adirect transition type which is on the substrate and which hassemi-insulating properties; a p-type semiconductor layer on at leastpart of the semiconductor layer; a first electrode which is electricallyconnected to the semiconductor layer and which is in contact with thep-type semiconductor layer; and a second electrode which is spaced apartfrom the first electrode and at least partially in contact with one ofthe semiconductor layer and the substrate. The first electrode includesa first opening part.

Such a first opening part can ensure the light-receiving area of thesemiconductor light receiving element. The first opening part permitsefficient light irradiation to the semiconductor layer and realizes agreat current of the semiconductor light receiving element.

Moreover, for example, the p-type semiconductor layer includes a secondopening part.

Such a second opening part permits a configuration such that the firstelectrode and the semiconductor layer exposed from the second openingpart are brought into direct contact with each other. The direct contactbetween the first electrode and the semiconductor layer makes itpossible to reduce the ON voltage of the pn-junction when thesemiconductor layer receives light. Moreover, the power consumption ofthe semiconductor light receiving element is reduced.

Moreover, for example, the p-type semiconductor layer is exposed fromthe first opening part.

Consequently, light can be irradiated to the p-type semiconductor layerfrom the first opening part.

Moreover, for example, the semiconductor layer is exposed from the firstopening part.

Consequently, light can be irradiated to the semiconductor layer exposedfrom the first opening part.

Moreover, for example, a border portion between the semiconductor layerand the p-type semiconductor layer is exposed from the first openingpart.

Consequently, the light can be irradiated to the semiconductor layer andthe p-type semiconductor layer exposed from the first opening part.

Moreover, for example, the second opening part includes a plurality ofopenings which are arranged side by side in a first direction, and eachof the plurality of openings is elongated in shape and long in a seconddirection crossing the first direction. The exposed part of thesemiconductor layer exposed from the second opening part includes: afirst region where the first electrode is provided on the exposed part;and a second region where the first electrode is not provided on theexposed part. The first region and the second region are locatedalternately in the first direction.

Consequently, the first region which contributes to the current and thesecond region for light uptake, both of which are in contact with thefirst electrode, are ensured in a well-balanced manner.

Moreover, for example, the first opening part includes a plurality offirst openings each of which is elongated in shape and long in a firstdirection, and the second opening part includes a plurality of secondopenings each of which is elongated in shape and long in a seconddirection crossing the first direction. The plurality of first openingsare arranged side by side in a direction crossing the first directionand the plurality of second opening are arranged side by side in adirection crossing the second direction. The semiconductor layer and thep-type semiconductor layer are exposed from each of the plurality offirst openings.

Such a first opening part more uniformly ensures the light receivingarea of the semiconductor layer and thus permits efficient lightirradiation to the semiconductor layer.

Moreover, for example, the first direction and the second direction areorthogonal to each other, the plurality of first openings are arrangedside by side in the second direction, and the plurality of secondopenings are arranged side by side in the first direction.

Such a first opening part more uniformly ensures the light receivingarea of the semiconductor layer and permits efficient light irradiationto the semiconductor layer.

Moreover, for example, the second opening part includes a plurality ofopenings each being annular in shape and the plurality of openings areconcentrically arranged. An exposed part of the semiconductor layerexposed from the second opening part includes: a first region where thefirst electrode is provided on the exposed part; and a second regionwhere the first electrode is not provided on the exposed part. The firstregion and the second region are located alternately in a radialdirection.

Consequently, the first region which contributes to the current and thesecond region for light uptake, both of which are in contact with thefirst electrode, are ensured in a well-balanced manner.

Moreover, for example, an active region of the semiconductor layer isrectangular in shape.

Consequently, the resistance of the semiconductor layer can be reducedas a result of light irradiation to the active region which isrectangular in shape.

Moreover, for example, the active region of the semiconductor layer iscircular in shape.

Consequently, the resistance of the semiconductor layer can be reducedas a result of light irradiation to the active region which is circularin shape.

Moreover, for example, the second electrode is on a bottom surface ofthe substrate.

Consequently, the semiconductor light receiving element can be realizedas a vertical device.

Moreover, for example, the second electrode is spaced apart from thefirst electrode on the semiconductor layer and at least partially incontact with the semiconductor layer.

Consequently, the semiconductor light receiving element can be realizedas a horizontal device.

Moreover, for example, the semiconductor layer has different impurityconcentrations in a stacking direction.

Consequently, a relatively high impurity concentration of a portion incontact with the first electrode suppresses the leak current when nolight is irradiated to the semiconductor layer.

Moreover, for example, the semiconductor layer includes: a firstsemiconductor layer; and a second semiconductor layer which is closer tothe substrate than the first semiconductor layer is, and the impurityconcentration of the first semiconductor layer is higher than theimpurity concentration of the second semiconductor layer.

Consequently, the leak current when no light is irradiated to thesemiconductor layer is suppressed.

Moreover, for example, the semiconductor layer includes a portion wherethe impurity concentration in the stacking direction continuouslychanges, and the impurity concentration in an uppermost region of theaforementioned portion is higher than the impurity concentrations inother regions of the aforementioned portion.

Consequently, the leak current when no light is irradiated to thesemiconductor layer is suppressed.

Moreover, for example, an impurity with which the semiconductor layer isdoped is carbon.

With the semiconductor layer to which carbon is doped as the impurity,the semi-insulating properties can be realized.

Moreover, for example, the semiconductor layer is formed based onIn_(x)Al_(y)Ga_((1-x-y))N (0≤x≤1, 0≤y≤1, and 0≤x+y≤1).

With the semiconductor layer formed of such a material, thesemi-insulating properties can be realized.

Moreover, for example, the substrate is a GAN substrate.

Consequently, with the GAN substrate, the semiconductor light receivingelement can be realized.

Moreover, the semiconductor relay according to one mode of the presentdisclosure includes: the semiconductor light receiving element describedabove; and a light emitting element which emits light toward thesemiconductor light receiving element.

The first opening part included in such a semiconductor relay can ensurethe light receiving area of the semiconductor light receiving element.The first opening part permits efficient light irradiation to thesemiconductor layer and realizes a great current of the semiconductorrelay.

Hereinafter, the embodiments will be described in detail with referenceto the drawings. Note that the embodiments described below eachillustrate a comprehensive and detailed example. Numerical values,shapes, materials, components, etc. illustrated in the embodiments beloweach form just one example and are not intended to limit the presentdisclosure in any manner. Moreover, among the components in theembodiments below, those not described in an independent claimindicating the highest concept will be described as optional components.

Moreover, each of the drawings is a schematic view and does notnecessarily provide a precise illustration. Note that substantially sameconfigurations are provided with same reference marks in each drawingand overlapping descriptions may be omitted or simplified.

Moreover, coordinate axes may be illustrated in the drawings used fordescribing the embodiments below. A Z-axis direction is expressed as avertical direction or a stacking direction, and a Z-axis+side may beexpressed as an upper side (top) and a Z-axis−side may be expressed as alower side (bottom). Moreover, an X-axis direction and a Y-axisdirection are directions orthogonal to each other on a planeperpendicular to the Z-axis direction. The X-axis direction may beexpressed as a horizontal direction. Hereinafter, a shape in a plan viewmeans a shape viewed from the Z-axis direction in the embodiments below(a shape viewed from a direction perpendicular to a main surface of thesubstrate).

Embodiment 1

First, the configuration of a semiconductor relay according toEmbodiment 1 will be described. FIG. 2 is a schematic sectional view ofthe semiconductor relay according to Embodiment 1. FIG. 3 is a top viewof a semiconductor light receiving element according to Embodiment 1.

As illustrated in FIGS. 2 and 3, semiconductor relay 10 according toEmbodiment 1 includes: light emitting element 20; and semiconductorlight receiving element 30 which is arranged oppositely to lightemitting element 20. Semiconductor relay 10 also includes four terminalsincluding input terminal 41, input terminal 42, output terminal 51, andoutput terminal 52. That is, semiconductor relay 10 is a four-terminalelement. Semiconductor relay 10 operates as a switch.

Light emitting element 20 emits light toward semiconductor lightreceiving element 30. Light emitting element 20 is formed by, forexample, a nitride semiconductor. More specifically, light emittingelement 20 is, for example, a light emitting diode which is formed by apn-junction of p-type InAlGaN and n-type InAlGaN. An n-type layer iselectrically connected with input terminal 41 and a p-type layer iselectrically connected with input terminal 42.

For example, an impurity such as Mg is doped as the p-type InAlGaN, andthe p-type InAlGaN is used which has a carrier concentration of 1E17cm⁻³ or more and 1E20 cm⁻³ or less. Moreover, an impurity such as Si orO is doped as the n-type InAlGaN and the n-type InAlGaN is used whichhas an impurity concentration of 1E16 cm⁻³ or more and 1E19 cm⁻³ orless.

Note that light emitting element 20 may be formed by a semiconductormaterial of a direct transition type other than InAlGaN. For example,light emitting element 20 may be formed by a material such as GaAs orZnSe.

Upon application of a voltage greater than or equal to the built-involtage of the pn-junction between input terminal 41 and input terminal42 in order to provide a higher potential of input terminal 42 than apotential of input terminal 41, a current flows to light emittingelement 20 whereby light emitting element 20 emits light.

Semiconductor light receiving element 30 includes substrate 31,semiconductor layer 32, first electrode 33, second electrode 34, andp-type semiconductor layer 36.

The shape of substrate 31 as a plate material formed with semiconductorlayer 32 may be, for example, rectangular in a plan view but may also becircular, and the shape of substrate 31 is thus not specificallylimited. Substrate 31 is, for example, a GaN substrate formed by GaN.Note that substrate 31 may be formed by a material such as Si, sapphire,SiC, or GaAs. Substrate 31 is formed by a conductive material inEmbodiment 1.

Semiconductor layer 32 is a semiconductor layer of a direct transitiontype which is on substrate 31 and which has semi-insulating properties.Semiconductor layer 32 has an active region A of a rectangular shape.Semiconductor layer 32 is formed by, for example, a nitridesemiconductor. More specifically, semiconductor layer 32 is formed by,for example, GaN. The thickness of semiconductor layer 32 is determinedbased on pressure resistance obtained for semiconductor light receivingelement 30 and a greater thickness of semiconductor layer 32 permitshigher pressure resistance. To realize a pressure resistance of severaltens to several hundreds of volts, the film thickness of semiconductorlayer 32 is, for example, 2 μm or more and 20 μm or less. Note thatsemiconductor layer 32 may be formed by using, for example, AlN, AlGaN,InN, InAlN, or InAlGaN other than GaN and may be formed of a pluralityof layers. Note that the semi-insulating properties means propertieswhich change from being insulating to being conductive, andsemiconductor layer 32 changes from being insulating to being conductiveas a result of light absorption.

P-type semiconductor layer 36 is a p-type semiconductor layer on theactive region A of semiconductor layer 32. More specifically, p-typesemiconductor layer 36 is formed by, for example, p-type GaN or p-typeInAlGaN.

Ever more specifically, for p-type semiconductor layer 36, for example,p-type GaN is used in which an impurity such as Mg is doped and whichhas a carrier concentration of 1E17 cm⁻³ or more and 1E20 cm⁻³ or less.The thickness of p-type semiconductor layer 36 is, for example, 400 nm.

P-type semiconductor layer 36 includes second opening part 136. Morespecifically, second opening part 136 includes a plurality of secondopenings 236. The plurality of second openings 236 are each elongated inshape and long in a Y-axis direction and are arranged side by side in anX-axis direction crossing the Y-axis direction. That is, second openingpart 136 is striped in shape. The X-axis direction is one example of afirst direction and the Y-axis direction is one example of a seconddirection. The top surface of semiconductor layer 32 is exposed fromsecond opening part 136. Note that the number of the plurality of secondopenings 236 included in second opening part 136 is not specificallylimited.

Semiconductor layer 32 is exposed from second opening part 136 insemiconductor light receiving element 30. That is, semiconductor layer32 is exposed from each of the plurality of second openings 236. Firstelectrode 33 can be in direct contact with semiconductor layer 32through second opening part 136.

P-type semiconductor layer 36 is formed, for example, in the followingmanner. First, continuous p-type semiconductor layer 36 is formed onsemiconductor layer 32. Next, continuous p-type semiconductor layer 36formed is partially removed through, for example, dry etching, wherebysecond opening part 136 is formed.

First electrode 33 is an electrode which is electrically connected tosemiconductor layer 32. More specifically, first electrode 33 is incontact with semiconductor layer 32 and p-type semiconductor layer 36 tocover p-type semiconductor layer 36 on semiconductor layer 32 (asemi-insulating InAlGaN layer). First electrode 33 is electricallyconnected to output terminal 51. More specifically, first electrode 33is formed by a Ti/Al-based material but may be formed by a differentmaterial. First electrode 33 may be formed by an ohmic material when incontact with semiconductor layer 32.

First electrode 33 includes first opening part 133. More specifically,first opening part 133 includes a plurality of first openings 233. Theplurality of first openings 233 are each elongated in shape and long inthe Y-axis direction and are arranged side by side in the X-axisdirection crossing the Y-axis direction. That is, first opening part 133is striped in shape. Such first opening part 133 can ensure the lightreceiving area of semiconductor layer 32.

P-type semiconductor layer 36 is exposed from first opening part 133 insemiconductor light receiving element 30. That is, p-type semiconductorlayer 36 is exposed from each of the plurality of first openings 233.Such first opening part 133 permits efficient light irradiation tosemiconductor layer 32.

Second electrode 34 is an electrode which is electrically connected tosemiconductor layer 32. Second electrode 34 is on a bottom surface ofsubstrate 31 and in contact with substrate 31. Second electrode 34 is,for example, across the entire bottom surface of semiconductor layer 32.More specifically, second electrode 34 is formed by a Ti/Al-basedmaterial but may be formed by a different material. Second electrode 34may be formed by an ohmic material when in contact with substrate 31.

Upon a decrease in the resistance of semiconductor layer 32 as a resultof light absorption of semiconductor layer 32, conduction between firstelectrode 33 and second electrode 34 occurs. Since first electrode 33and second electrode 34 are vertically arrayed at this point, a currentflow vertically.

[Detailed Configuration of Semiconductor Layer]

Next, the detailed configuration of semiconductor layer 32 will bedescribed. Semiconductor layer 32 (a semi-insulating InAlGaN layer) isdoped with: a first impurity of an acceptor type which forms a deepacceptor level; and a second impurity of a donor type. The firstimpurity is, for example, Fe (iron) or C (carbon) and the secondimpurity is, for example, Si (silicon) or O (oxygen).

Here, it is known that an element like C (the first impurity of anacceptor type), which forms the deep acceptor level, compensates Si asthe second impurity of a donor type. That is, the use of the elementlike C as an impurity compensates concentration Si corresponding toconcentration C.

To realize the semi-insulating properties of semiconductor layer 32, theconcentration Na of the first impurity of an acceptor type which formsthe deep acceptor level is higher than the concentration Nd of thesecond impurity of a donor type.

For example, the impurities may be doped to the nitride semiconductorforming semiconductor layer 32 in a manner such that the concentrationobtained by subtracting the concentration Nd of the second impurity ofthe donor type from the concentration Na of the first impurity of theacceptor type (the concentration Na−the concentration Nd) is within arange between 0.5E16 cm⁻³ or more and 1E19 cm⁻³ or less. Moreover, theproperties are more improved by doping the nitride semiconductor formingsemiconductor layer 32 with the impurities within the range between 1E16cm⁻³ or more and 1E18 cm⁻³ or less.

The resistivity of semiconductor layer 32 is, for example, 1×10⁵ Ωcm ormore in a state in which semiconductor layer 32 receives no light. Theresistivity of semiconductor layer 32 is lower when semiconductor layer32 receives light from light emitting element 20 than when semiconductorlayer 32 receives no light. When the intensity of incident light issufficiently large, the resistivity of semiconductor layer 32 decreasesto approximately 0.01 Ωcm or more and 1 Ωcm or less. That is,semiconductor layer 32 switches from being insulative to beingconductive as a result of absorbing the light from light emittingelement 20.

Note that the above InAlGaN represents 4-element mixed crystalIn_(x)Al_(y)Ga_((1-x-y))N (where x and y are any values satisfying0≤x≤1, 0≤y≤1, and 0≤x+y≤1). Hereinafter, the multiple-element mixedcrystal is abbreviated based on the sequence of constituent elementsymbols. That is, subscripts are omitted.

Operation

Next, the operation of semiconductor relay 10 will be described. When avoltage of 0 V is applied between input terminal 41 and input terminal42, that is, no voltage is applied between input terminal 41 and inputterminal 42, light emitting element 20 is emitting no light (a light-OFFstate). In this state, semiconductor layer 32 has very high resistanceand thus little current flows between output terminal 51 and outputterminal 52.

On the other hand, upon application of a voltage, which becomes aforward bias for the pn junction, between input terminal 41 and inputterminal 42, light emitting element 20 emits light (lights up). As aresult of light absorption by semiconductor layer 32 in this state, anelectron-hole pair is generated inside semiconductor layer 32. That is,the electron-hole pair is excited inside semiconductor layer 32. Thegenerated electron-hole pair acts as a carrier and the band structure ofsemiconductor layer 32 is modulated, thus leading to low resistance.Therefore, a great current flows between output terminal 51 and outputterminal 52. Note that semiconductor relay 10 has bidirectionality,which permits current flows both from output terminal 51 to outputterminal 52 and from output terminal 52 to output terminal 51.

Note that the wavelength of the light emitted by light emitting element20 needs to be less than or equal to the light absorption wavelength ofsemiconductor layer 32 (light receiving region 35) since the lightabsorption does not occur if the wavelength of the light emitted bylight emitting element 20 is longer than the light absorption wavelengthof semiconductor layer 32.

[Effects Provided by p-type Semiconductor Layer]

Next, the effects provided by p-type semiconductor layer 36 will bedescribed. In semiconductor relay 10, when light emitting element 20lights off (that is, semiconductor light receiving element 30 is in anOFF state), a reverse voltage is applied to a pn-junction of p-typesemiconductor layer 36 and semiconductor layer 32, so that a depletionlayer extends from an interface between p-type semiconductor layer 36and semiconductor layer 32.

Consequently, the electric field for the interface between firstelectrode 33 and semiconductor layer 32 can be alleviated. Thus, it ispossible to improve the pressure resistance of semiconductor lightreceiving element 30 and also reduce the leak current. Note that theeffects of the pressure resistance improvement and the leak currentreduction are greater with an increase in the width of second openings236 of p-type semiconductor layer 36, and thus the width of secondopenings 236 of p-type semiconductor layer 36 is preferably 2 μm orless.

[Effects Provided by First Opening Part]

Next, the effects provided by first opening part 133 will be described.A current flows through semiconductor light receiving element 30 as aresult of a decrease in the resistance of semiconductor layer 32 onlywhen semiconductor light receiving element 30 is irradiated with light.Therefore, a great current can be expected by increasing the lightreceiving area of semiconductor layer 32 in semiconductor lightreceiving element 30.

Here, covering the top of semiconductor layer 32 with first electrode 33as illustrated in FIG. 1 reduces the light receiving area ofsemiconductor layer 32, causing a problem that a sufficient currentcannot be provided. On the other hand, first electrode 33 andsemiconductor layer 32 needs to be in contact with each other in orderto immediately transport, as a current, the carrier generated insidesemiconductor layer 32.

Thus, in semiconductor light receiving element 30, first electrode 33includes first opening part 133 which exposes the top surface of p-typesemiconductor layer 36. Consequently, semiconductor layer 32 can receivelight through first opening part 133.

Light incident on semiconductor layer 32 spreads inside semiconductorlayer 32. Thus, first opening part 133 permits the excitation of theelectron-hole pair even in a portion located under first electrode 33.Note that, however, a large width of first electrode 33 can form anactive region where no electron-hole pair is generated, and thus thewidth of first electrode 33 is preferably 5 μm or less.

As described above, first opening part 133 can ensure the lightreceiving area of semiconductor light receiving element 30. Thus, lightis efficiently irradiated to semiconductor layer 32 and the resistanceof semiconductor layer 32 more decreases, which therefore realizes greatcurrent operation of semiconductor light receiving element 30.

Note that the top surface of p-type semiconductor layer 36 is exposedfrom first opening part 133 and the inner circumferential surface (aninclined side surface in FIG. 2) of p-type semiconductor layer 36forming second openings 236 is covered with first electrode 33. That is,first electrode 33 is not only in contact with semiconductor layer 32through second opening part 136 provided in p-type semiconductor layer36 but also in contact with the inner circumferential surface of p-typesemiconductor layer 36 forming second openings 236.

Consequently, it is possible to apply a voltage to the pn-junctionformed by semiconductor layer 32 and p-type semiconductor layer 36. Asdescribed above, the depletion layer is formed as a result of theapplication of the reverse voltage to the pn-junction, which thereforemakes it possible to improve the dielectric voltage of semiconductorlight receiving element 30. Moreover, it is possible to reduce the leakcurrent.

Variation 1

Next, the configuration of a semiconductor relay according to Variation1 will be described. FIG. 4 is a schematic sectional view of thesemiconductor relay according to Variation 1. FIG. 5 is a top view of asemiconductor light receiving element according to Variation 1. Notethat Variation 1 will be described below, focusing on a difference fromsemiconductor relay 10, and those already described will be omitted fromthe description as appropriate. The same applies to Variations 2 to 6below.

As illustrated in FIG. 4, semiconductor relay 10 a includes lightemitting element 20 and semiconductor light receiving element 30 a whichis arranged oppositely to light emitting element 20. Semiconductor relay10 a also includes four terminals including input terminal 41, inputterminal 42, output terminal 51, and output terminal 52.

As illustrated in FIGS. 4 and 5, semiconductor light receiving element30 a includes substrate 31, semiconductor layer 32, first electrode 33a, second electrode 34, and p-type semiconductor layer 36.

First electrode 33 a includes first opening part 133 a. Morespecifically, first opening part 133 a includes a plurality of firstopenings 233 a. The plurality of first openings 233 a are each elongatedin shape and long in a Y-axis direction and are arranged side by side inan X-axis direction crossing the Y-axis direction.

Each of the plurality of first openings 233 a is located inside secondopenings 236 in a plan view. As a result, semiconductor layer 32 isexposed from each of the plurality of first openings 233 a. Such firstopening part 133 a ensures the light receiving area of semiconductorlayer 32 and permits efficient light irradiation to semiconductor layer32.

Note that first electrode 33 a covers the top surface of p-typesemiconductor layer 36, the inner circumferential surface (an inclinedside surface in FIG. 4) of p-type semiconductor layer 36 forming secondopenings 236, and part of semiconductor layer 32 exposed from secondopenings 236 in semiconductor light receiving element 30 a. That is,first electrode 33 a is in contact with both semiconductor layer 32 andp-type semiconductor layer 36.

Consequently, semiconductor light receiving element 30 a can immediatelytransport, as a current, a carrier generated inside semiconductor layer32. Moreover, the application of a reverse voltage to a pn-junctionformed by semiconductor layer 32 and p-type semiconductor layer 36improves the dielectric voltage of semiconductor light receiving element30 a and also can reduce the leak current.

Variation 2

Next, the configuration of a semiconductor relay according to Variation2 will be described. FIG. 6 is a schematic sectional view of thesemiconductor relay according to Variation 2. FIG. 7 is a top view of asemiconductor light receiving element according to Variation 2.

As illustrated in FIG. 6, semiconductor relay 10 b includes lightemitting element 20 and semiconductor light receiving element 30 b whichis arranged oppositely to light emitting element 20. Semiconductor relay10 b also includes four terminals including input terminal 41, inputterminal 42, output terminal 51, and output terminal 52.

As illustrated in FIGS. 6 and 7, semiconductor light receiving element30 b includes substrate 31, semiconductor layer 32, first electrode 33b, second electrode 34, and p-type semiconductor layer 36.

First electrode 33 b includes first opening part 133 b. Morespecifically, first opening part 133 b includes a plurality of firstopenings 233 b. The plurality of first openings 233 b are each elongatedin shape and long in a Y-axis direction and arranged side by side in anX-axis direction crossing the Y-axis direction.

Semiconductor layer 32 and p-type semiconductor layer 36 are exposedfrom first opening part 133 b. That is, semiconductor layer 32 andp-type semiconductor layer 36 are exposed from each of the plurality offirst openings 233 b. Such first opening part 133 b ensures the lightreceiving area of semiconductor layer 32 and permits efficient lightirradiation to semiconductor layer 32.

Note that first electrode 33 b covers part of the top surface of p-typesemiconductor layer 36 and part of semiconductor layer 32 exposed fromsecond openings 236 in semiconductor light receiving element 30 b. Thatis, first electrode 30 b is in contact with both semiconductor layer 32and p-type semiconductor layer 36.

Consequently, semiconductor light receiving element 30 b can immediatelytransport, as a current, a carrier generated inside semiconductor layer32. Moreover, the application of a reverse voltage to a pn-junctionformed by semiconductor layer 32 and p-type semiconductor layer 36 canimprove the dielectric voltage of semiconductor light receiving element30 b and also can reduce the leak current.

Note that, as illustrated in FIG. 7, a border portion betweensemiconductor layer 32 and p-type semiconductor layer 36 is exposed fromfirst opening part 133 b. More specifically, the border portion betweensemiconductor layer 32 and p-type semiconductor layer 36 is exposed fromeach of the plurality of first openings 233 b. That is, the innercircumferential surface (an inclined side surface in FIG. 6) of p-typesemiconductor layer 36 forming second openings 236 is exposed from firstopening part 133 b.

When a portion of p-type semiconductor layer 36 located between twosecond openings 236 is mesa-shaped, the border portion betweensemiconductor layer 32 and p-type semiconductor layer 36 is likely toface dielectric breakdown due to electric field concentration. As aresult of exposing the border portion from first opening part 133 b,first electrode 33 b is not in a portion where the electric fieldconcentration is likely to occur, which permits an improvement in thedielectric voltage.

Variation 3

Next, the configuration of a semiconductor relay according to Variation3 will be described. FIG. 8 is a schematic sectional view of thesemiconductor relay according to Variation 3. FIG. 9 is a top view of asemiconductor light receiving element according to Variation 3.

As illustrated in FIG. 8, semiconductor relay 10 c includes lightemitting element 20 and semiconductor light receiving element 30 c whichis arranged oppositely to light emitting element 20. Semiconductor relay10 c also includes four terminals including input terminal 41, inputterminal 42, output terminal 51, and output terminal 52.

As illustrated in FIGS. 8 and 9, semiconductor light receiving element30 c includes substrate 31, semiconductor layer 32, first electrode 33c, second electrode 34, and p-type semiconductor layer 36.

First electrode 33 c includes first opening part 133 c. Morespecifically, first opening part 133 c includes a plurality of firstopenings 233 c which are arranged side by side in an X-axis direction.The plurality of first openings 233 c are each rectangular in shape andlong in a Y-axis direction. The X-axis direction is one example of thefirst direction and the Y-axis direction is one example of the seconddirection.

An exposed part of semiconductor layer 32 exposed from second openingpart 136 includes: a first region where first electrode 33 c is providedon the exposed part; and a second region where first electrode 33 c isnot provided on the exposed part. The first region and the second regionare located alternately in the X-axis direction.

Consequently, semiconductor light receiving element 30 c can immediatelytransport, as a current, a carrier generated inside semiconductor layer32. Moreover, the application of a reverse voltage to a pn-junctionformed by semiconductor layer 32 and p-type semiconductor layer 36improves the dielectric voltage of semiconductor light receiving element30 c and can reduce the leak current.

Moreover, the first region which contributes to the current and thesecond region for light uptake, both of which are in contact with firstelectrode 33 c, are ensured in a well-balanced manner in semiconductorlight receiving element 30 c. Note that the first region and the secondregion may not necessarily be alternately located. The two or more firstregions may be arranged side by side between the two second regions.

Variation 4

Next, the configuration of a semiconductor light receiving elementaccording to Variation 4 will be described. FIG. 10 is a top view of thesemiconductor light receiving element according to Variation 4. FIG. 11is a schematic sectional view of the semiconductor light receivingelement according to Variation 4, taken along line XI-XI of FIG. 10.FIG. 12 is a schematic sectional view of the semiconductor lightreceiving element according to Variation 4, taken along line XII-XII ofFIG. 10.

As illustrated in FIGS. 10 to 12, semiconductor light receiving element30 d includes substrate 31, semiconductor layer 32, first electrode 33d, second electrode 34, and p-type semiconductor layer 36.

First electrode 33 d includes first opening part 133 d. Morespecifically, first opening part 133 d includes a plurality of firstopenings 233 d. The plurality of first openings 233 d are each elongatedin shape and long in an X-axis direction and are arranged side by sidein a Y-axis direction crossing the X-axis direction. The X-axisdirection is one example of the first direction and the Y-axis directionis one example of the second direction.

Note that second opening part 136 includes a plurality of secondopenings 236 which are elongated in shape and long in the Y-axisdirection crossing the X-axis direction. The plurality of secondopenings 236 are arranged side by side in the X-axis direction crossingthe Y-axis direction.

The plurality of first openings 233 d cross the plurality of secondopenings 236 in a plan view. In other words, the stripe direction offirst opening part 133 d (that is, the X-axis direction) and the stripedirection of second opening part 136 (that is, the Y-axis direction)cross each other at an angle. As a result, semiconductor layer 32 andp-type semiconductor layer 36 are exposed from each of first openings233 d.

Such first opening part 133 d more uniformly ensures the light receivingarea of semiconductor layer 32 and permits efficient light irradiationto semiconductor layer 32.

Moreover, first electrode 33 d is across semiconductor layer 32 andp-type semiconductor layer 36 in semiconductor light receiving element30 d. Consequently, first electrode 33 d can be formed without beingaffected by the shape of p-type semiconductor layer 36 and the stripeinterval of second opening part 136. In other words, the degree offreedom in device fabrication can be increased.

Note that the stripe direction of first opening part 133 d and thestripe direction of second opening part 136 do not have to be orthogonalto each other as long as the two stripe directions cross each other atan angle. That is, where first openings 233 d is long in the firstdirection, second openings 236 d may be long in the second directioncrossing the first direction.

Variation 5

Next, the configuration of a semiconductor light receiving elementaccording to Variation 5 will be described. FIG. 13 is a top view of thesemiconductor light receiving element according to Variation 5.Variation 5 will be described below, focusing on a difference fromsemiconductor light receiving element 30, and those already describedwill be omitted from the description as appropriate.

As illustrated in FIG. 13, semiconductor light receiving element 30 eincludes substrate 31 (not illustrated), semiconductor layer 32, firstelectrode 33 e, second electrode 34, and p-type semiconductor layer 36.

First electrode 3 e includes first opening part 133 e. Morespecifically, first opening part 133 e includes a plurality of firstopenings 233 e. The plurality of first openings 233 e are each elongatedin shape and long in a Y-axis direction and are arranged side by side inan X-axis direction crossing the Y-axis direction.

First opening part 33 e has a pad region B. The pad region B is arectangular region for bonding a wire for electric connection of outputterminal 51 and first electrode 33 e and is located within an activeregion A in a plan view. The pad region B is provided on a relativelyouter side in first electrode 33 e. Consequently, the interference oflight uptake through first opening part 133 e by the pad region B issuppressed. That is, the amount of light uptake through first openingpart 133 e is improved.

Note that the shape, size, and arrangement of the pad region are notspecifically limited. For example, the pad region B may be providedoutside of the active region A in a plan view. Consequently, theinterference of the light uptake through first opening part 133 e by thepad region B is suppressed.

Variation 6

Next, the configuration of a semiconductor light receiving elementaccording to Variation 6 will be described. FIGS. 14 and 15 are topviews of the semiconductor light receiving element according toVariation 6. FIG. 14 is a plan view obtained by removing third electrode37 from FIG. 15. Variation 6 will be described below, focusing on adifference from semiconductor light receiving element 30, and thosealready described will be omitted from the description as appropriate.

As illustrated in FIGS. 14 and 15, semiconductor light receiving element30 f includes a substrate (not illustrated), semiconductor layer 32 f,first electrode 33 f, a second electrode (not illustrated), p-typesemiconductor layer 36 f, and third electrode 37.

Semiconductor layer 32 f is a semiconductor layer of a direct transitiontype which is on the substrate and which has semi-insulating properties.Semiconductor layer 32 f has an active region C which is circular inshape. The shape of semiconductor layer 32 f in a plan view issubstantially circular and is partially projected outward for a padregion D.

P-type semiconductor layer 36 f is a p-type semiconductor layer on theactive region C of semiconductor layer 32 f P-type semiconductor layer36 f is circular in a plan view.

P-type semiconductor layer 36 f includes second opening part 136 f. Morespecifically, second opening part 136 f includes a plurality of secondopenings 236 f. The plurality of second openings 236 f are each annularin shape and are concentrically arranged.

First electrode 33 f includes first opening part 133 f. Morespecifically, first opening part 133 f includes a plurality of firstopenings 233 f. The plurality of first openings 233 f are each annularin shape and are concentrically arranged. P-type semiconductor layer 36f is exposed from first opening part 133 f.

Third electrode 37 is an electrode which is located on first electrode33 f and which electrically connect first electrode 33 f divided byfirst opening part 133 f. Third electrode 37 has a pad region D. The padregion D is a rectangular region for bonding a wire for electricconnection of output terminal 51 and first electrode 33 f and is locatedoutside the active region C in a plan view.

Even in such semiconductor light receiving element 30 f havingsemiconductor layer 32 f which is substantially circular in shape, firstopening part 133 f ensures the light receiving area of semiconductorlayer 32 f and permits efficient light irradiation to semiconductorlayer 32 f.

Note that first electrode 33 f is arranged on semiconductor layer 32 fexposed from second opening part 136 f in semiconductor light receivingelement 30 f, but first electrode 33 f may not necessarily be arrangedon semiconductor layer 32 f exposed from second opening part 136 f. FIG.16 is a top view of such semiconductor light receiving element 30 g.

In semiconductor light receiving element 30 g, an exposed part ofsemiconductor layer 32 f exposed from second opening part 136 fincludes: a first region where first electrode 33 g is provided on theexposed part; and a second region where first electrode 33 g is notprovided on the exposed part. The first and second regions are locatedalternately in a radial direction. Consequently, the same effects asthose provided by semiconductor light receiving element 30 c areprovided.

Note that the first region and the second region may not necessarily bealternately located. The two or more first regions may be arranged sideby side between the two second regions.

Moreover, the shape of the semiconductor light receiving element in aplan view is not limited to a rectangular or circular shape. The shapeof the semiconductor light receiving element in a plan view may be, forexample, polygonal or oval. Moreover, for example, a plurality ofsemiconductor light receiving elements which are rectangular or circularin shape may be superposed on each other and the elements may beelectrically connected together.

Modified Example of First Opening Part

Note that first openings 233 forming first opening part 133 are notlimited to closed openings. For example, like semiconductor lightreceiving element 30 h illustrated in FIG. 17, each of a plurality offirst openings 233 h forming first opening part 133 h may be a notchprovided at first electrode 33 h. Moreover, like semiconductor lightreceiving element 30 i illustrated in FIG. 18, a plurality of firstopenings 233 i forming first opening part 133 i may be a region betweenfirst electrodes 33 i of an island shape. FIGS. 17 and 18 are plan viewsof semiconductor light receiving elements for explaining the modifiedexamples of the first opening part.

As described above, first openings 233 are not limited to closedopenings. Note that the area of first opening part 133 with respect tothe area of first electrode 33 in a plan view may be, for example, 30%or more and 70% or less.

Note that as is the case with semiconductor light receiving element 30f, semiconductor light receiving element 30 i includes a third electrodewhich electrically connects first electrodes 33 i of the island shape.

[Horizontal Device]

The semiconductor light receiving element realized as a vertical devicehas been described in the embodiment above, but the semiconductor lightreceiving element may be realized as a horizontal device. FIG. 19 is aschematic sectional view of the semiconductor light receiving elementrealized as a horizontal device.

Second electrode 34 included in semiconductor light receiving element 30j illustrated in FIG. 19 is on the top surface of semiconductor layer 32spaced apart from first electrode 33. Second electrode 34 is provided tocover part of the top surface of semiconductor layer 32. Note thatsecond electrode 34 may be on substrate 31 exposed by removing part ofsemiconductor layer 32 through, for example, dry etching.

Upon light irradiation to semiconductor layer 32, semiconductor layer 32causes conduction between first electrode 33 (output terminal 51) andsecond electrode 34 (output terminal 52). Since first electrode 33 andsecond electrode 34 are arrayed in a horizontal direction at this point,a current flows in the horizontal direction. That is, semiconductorlight receiving element 30 j is a horizontal device.

Also in such semiconductor light receiving element 30 j, first openingpart 133 ensures the light receiving area of semiconductor layer 32 andpermits efficient light irradiation to semiconductor layer 32.

Moreover, second electrode 34 may have the same configuration as theconfiguration of first electrode 33. FIG. 20 is a schematic sectionalview of another semiconductor light receiving element realized as ahorizontal device.

P-type semiconductor layer 38 included in semiconductor light receivingelement 30 k illustrated in FIG. 20 is a p-type semiconductor layer onsemiconductor layer 32. As is the case with p-type semiconductor layer36, p-type semiconductor layer 38 includes a second opening part. Thesecond opening part is striped in shape.

Second electrode 34 k included in semiconductor light receiving element30 k is in contact with semiconductor layer 32 and p-type semiconductorlayer 36 to cover p-type semiconductor layer 38. Second electrode 34 kincludes third opening part 133 k. Third opening part 133 k is stripedin shape. Such third opening part 133 k can ensure the light receivingarea of semiconductor layer 32. Moreover, since a pn-junction of p-typesemiconductor layer 38 and semiconductor layer 32 is under secondelectrode 34 k, semiconductor light receiving element 30 k has favorablebidirectionality.

Note that substrate 31 may not have conductivity in the semiconductorlight receiving element realized as the horizontal device. Substrate 31may be, for example, a sapphire substrate.

[Impurity Concentration for Suppressing Leak Current]

When the semiconductor relay or the semiconductor light receivingelement is a vertical device, it is also possible to suppress the leakcurrent by making the impurity concentration in the semiconductor layerbiased in a vertical direction (in other words, a stacking direction).That is, the semiconductor layer may have different impurityconcentrations in the stacking direction. FIG. 21 is a schematicsectional view of such a semiconductor relay.

Semiconductor relay 101 illustrated in FIG. 21 includes light emittingelement 20 and semiconductor light receiving element 30 l which isarranged oppositely to light emitting element 20. Semiconductor layer 32l included in semiconductor light receiving element 30 l includes firstsemiconductor layer 32 l 1 and second semiconductor layer 32 l 2. Secondsemiconductor layer 32 l 2 is on substrate 31 and first semiconductorlayer 32 l 1 is on second semiconductor layer 32 l 2. That is,semiconductor layer 32 l includes first semiconductor layer 32 l 1 andsecond semiconductor layer 32 l 2 which is closer to substrate 31 thanfirst semiconductor layer 32 l 1 is.

Here, the impurity concentration of first semiconductor layer 32 l 1 ishigher than the impurity concentration of second semiconductor layer 32l 2. That is, the impurity concentration becomes higher toward the topside of semiconductor layer 32 l (first electrode 33 side).

Consequently, when no light is irradiated to semiconductor lightreceiving element 30 l and when a reverse voltage is applied betweenfirst electrode 33 and second electrode 34, a depletion layer is likelyto extend inside semiconductor layer 32 l, which makes it possible tokeep the dielectric voltage high. Therefore, it is possible to suppressthe leak current.

Moreover, when light is irradiated to semiconductor light receivingelement 30 l, the resistance of second semiconductor layer 32 l 2sufficiently decreases and a current is likely to flow. As a result,semiconductor light receiving element 30 l can be realized whichprovides a high ON-OFF ratio.

Note that semiconductor layer 32 l has a two-layer structure but mayhave a structure in which three or more layers are stacked. The effectof suppressing the leak current is also provided in this case if theimpurity concentration becomes higher toward the top side.

Moreover, the semiconductor layer includes a portion where the impurityconcentration in the stacking direction continuously changes, and theimpurity concentration may be high in an uppermost region of theaforementioned portion than in other regions of the aforementionedportion. For example, the impurity concentration may become highertoward the top side in a single-layered semiconductor layer. FIG. 22 isa schematic sectional view of such a semiconductor relay.

Semiconductor relay 10 m illustrated in FIG. 22 includes light emittingelement 20 and semiconductor light receiving element 30 m which isarranged oppositely to light emitting element 20. In semiconductor lightreceiving element 30 m, semiconductor layer 32 m is single-layered andthe impurity concentration inside semiconductor layer 32 m is biased.More specifically, the impurity concentration becomes higher toward thetop side inside semiconductor layer 32 m. Note that being single-layeredmeans, for example, that an interface perpendicular to the stackingdirection is not inside semiconductor layer 32 m. Inside semiconductorlayer 32 m, the impurity concentration of a portion in contact withfirst electrode 33 may be relatively high. That is, semiconductor layer32 m may include, under the portion in contact with first electrode 33,a region where the impurity concentration is lower than in the portionin contact with first electrode 33.

Consequently, when no light is irradiated to semiconductor lightreceiving element 30 m and when a reverse voltage is applied betweenfirst electrode 33 and second electrode 34, a depletion layer is likelyto extend inside semiconductor layer 32 m, which makes it possible tokeep the dielectric voltage high. Therefore, it is possible to suppressthe leak current.

Moreover, when light is irradiated to semiconductor light receivingelement 30 m, the resistance of a portion of semiconductor layer 32 m onthe top side sufficiently decreases and a current is likely to flow. Asa result, semiconductor light receiving element 30 m can be realizedwhich provides a high ON-OFF ratio.

Note that the bias of the impurity concentration in semiconductor layer32 m can be realized by, for example, changing the temperature ofsubstrate 31 during the crystal growth of semiconductor layer 32 m.Moreover, the bias of the impurity concentration in semiconductor layer32 m may be realized by a process such as impurity injection ordiffusion.

Other Embodiment

The semiconductor light receiving elements and the semiconductor relaysaccording to one or a plurality of modes have been described above basedon the embodiment, but the present disclosure is not limited to theembodiment described above.

For example, the number of first openings included in the first openingpart, the shape of the first openings, etc. in the embodiment describedabove are each one example and are not specifically limited. The sameapplies to the number of second openings included in the second openingpart and the shape of the second openings.

Moreover, the stacking structure illustrated in the schematic sectionalviews of the embodiment described above is one example and the presentdisclosure is not limited to the aforementioned stacking structure. Thatis, as is the case with the stacking structure illustrated in theschematic sectional views of the embodiment described above, the presentdisclosure also includes a stacking structure which can realize thecharacteristic functions of the present disclosure. For example, anotherlayer may be provided between the layers of the aforementioned stackingstructure within a scope in which the same functions as the functions ofthe aforementioned stacking structure can be realized.

Moreover, the aforementioned embodiment illustrates main materialsforming the layers of the stacking structure but each layer of thestacking structure may include a different material within a scope inwhich the same functions as the functions of the aforementioned stackingstructure can be realized.

Moreover, in the embodiment described above, the semiconductor lightreceiving elements are used in the semiconductor relays but may be usedto different applications such as a UV sensor which reacts toultraviolet light with an emission peak wavelength of around 365 nm.

Additionally, the present disclosure also includes: a mode obtained bymaking various modifications conceivable by those skilled in the art toeach embodiment; or a mode realized by making desired combinations ofthe components and the functions in each embodiment within a scope notdeparting from the spirits of the present disclosure. For example, thepresent disclosure may be realized as, for example, an integratedcircuit having the aforementioned semiconductor relay.

INDUSTRIAL APPLICABILITY

The semiconductor light receiving elements of the present disclosure areeach useful as a power device used in a power supply circuit of aconsumer device or a UV sensor which reacts to ultraviolet light.

REFERENCE MARKS IN THE DRAWINGS

10, 10a, 10b, 10c, 10l, 10m, 10z semiconductor layer 20 light emittingelement 30, 30a, 30b, 30c, 30d, 30e, 30f, semiconductor light 30g, 30h,30i, 30j, 30k, 30l, receiving element 30m, 30z 31 substrate 32, 32f,32l, 32m semiconductor layer 32l1 first semiconductor layer 32l2 secondsemiconductor layer 33, 33a, 33b, 33c, 33d, 33e, 33f, first electrode33g, 33h, 33i 34, 34k second electrode 35 light receiving region 36,36f, 38 p-type semiconductor layer 37 third electrode 41, 42 inputterminal 51, 52 output terminal 133, 133a, 133b, 133c, 133d, firstopening part 133e, 133f, 133h, 133i 133k third opening part 136, 136fsecond opening part 233, 233a, 233b, 233c, 233d, first opening 233e,233f, 233h, 233i 236, 236d, 236f second opening A, C active region B, Dpad region

The invention claimed is:
 1. A semiconductor light receiving element,comprising: a substrate; a semiconductor layer of a direct transitiontype on the substrate, the semiconductor layer having semi-insulatingproperties; a p-type semiconductor layer on at least part of thesemiconductor layer; a first electrode electrically connected to thesemiconductor layer and in contact with the p-type semiconductor layer;and a second electrode spaced apart from the first electrode and atleast partially in contact with one of the semiconductor layer and thesubstrate, wherein the first electrode includes a first opening part,the p-type semiconductor layer includes a second opening part, thesecond opening part includes a plurality of openings arranged side byside in a first direction, each of the plurality of openings iselongated in shape and long in a second direction crossing the firstdirection, an exposed part of the semiconductor layer exposed from thesecond opening part includes: a first region where the first electrodeis provided on the exposed part; and a second region where the firstelectrode is not provided on the exposed part, and the first region andthe second region are located alternately in the first direction.
 2. Thesemiconductor light receiving element according to claim 1, wherein thep-type semiconductor layer is exposed from the first opening part. 3.The semiconductor light receiving element according to claim 1, whereinthe semiconductor layer is exposed from the first opening part.
 4. Thesemiconductor light receiving element according to claim 1, wherein aborder portion between the semiconductor layer and the p-typesemiconductor layer is exposed from the first opening part.
 5. Thesemiconductor light receiving element according to claim 1, wherein anactive region of the semiconductor layer is rectangular.
 6. Thesemiconductor light receiving element according to claim 1, wherein anactive region of the semiconductor layer is circular.
 7. Thesemiconductor light receiving element according to claim 1, wherein thesecond electrode is provided on a bottom surface of the substrate. 8.The semiconductor light receiving element according to claim 1, whereinthe semiconductor layer has different impurity concentrations in astacking direction.
 9. The semiconductor light receiving elementaccording to claim 8, wherein an impurity with which the semiconductorlayer is doped is carbon.
 10. The semiconductor light receiving elementaccording to claim 1, wherein the semiconductor layer is formed based onIn_(x)Al_(y)Ga_((1-x-y))N, where 0≤x≤1, 0≤y≤1, and 0≤x+y≤1.
 11. Thesemiconductor light receiving element according to claim 1, wherein thesubstrate is a GAN substrate.
 12. A semiconductor relay, comprising: thesemiconductor light receiving element according to claim 1; and a lightemitting element which emits light toward the semiconductor lightreceiving element.
 13. A semiconductor light receiving element,comprising: a substrate; a semiconductor layer of a direct transitiontype on the substrate, the semiconductor layer having semi-insulatingproperties; a p-type semiconductor layer on at least part of thesemiconductor layer; a first electrode electrically connected to thesemiconductor layer and in contact with the p-type semiconductor layer;and a second electrode spaced apart from the first electrode and atleast partially in contact with one of the semiconductor layer and thesubstrate, wherein the first electrode includes a first opening part,the p-type semiconductor layer includes a second opening part, the firstopening part includes a plurality of first openings each of which iselongated in shape and long in the first direction, the second openingpart includes a plurality of second openings each of which is elongatedin shape and long in the second direction crossing the first direction,the plurality of first openings are arranged side by side in a directioncrossing the first direction, the plurality of second openings arearranged side by side in a direction crossing the second direction, andthe semiconductor layer and the p-type semiconductor layer are exposedfrom each of the plurality of first openings.
 14. The semiconductorlight receiving element according to claim 13, wherein the firstdirection and the second direction are orthogonal to each other, theplurality of first openings are arranged side by side in the seconddirection, and the plurality of second openings are arranged side byside in the first direction.
 15. A semiconductor relay, comprising: thesemiconductor light receiving element according to claim 13, and a lightemitting element which emits light toward the semiconductor lightreceiving element.
 16. A semiconductor light receiving element,comprising: a substrate; a semiconductor layer of a direct transitiontype on the substrate, the semiconductor layer having semi-insulatingproperties; a p-type semiconductor layer on at least part of thesemiconductor layer; a first electrode electrically connected to thesemiconductor layer and in contact with the p-type semiconductor layer;and a second electrode spaced apart from the first electrode and atleast partially in contact with one of the semiconductor layer and thesubstrate, wherein the first electrode includes a first opening part,and the second electrode is provided on the semiconductor layer, spacedapart from the first electrode and at least partially in contact withthe semiconductor layer.
 17. A semiconductor relay, comprising: thesemiconductor light receiving element according to claim 16, and a lightemitting element which emits light toward the semiconductor lightreceiving element.
 18. A semiconductor light receiving element,comprising: a substrate; a semiconductor layer of a direct transitiontype on the substrate, the semiconductor layer having semi-insulatingproperties; a p-type semiconductor layer on at least part of thesemiconductor layer; a first electrode electrically connected to thesemiconductor layer and in contact with the p-type semiconductor layer;and a second electrode spaced apart from the first electrode and atleast partially in contact with one of the semiconductor layer and thesubstrate, wherein the first electrode includes a first opening part,the second electrode is provided on a bottom surface of the substrate,the semiconductor layer includes: a first semiconductor layer; and asecond semiconductor layer closer to the substrate than the firstsemiconductor layer is, and an impurity concentration of the firstsemiconductor layer is higher than an impurity concentration of thesecond semiconductor layer.
 19. The semiconductor light receivingelement according to claim 18, wherein the p-type semiconductor layerincludes a second opening part, the second opening part includes aplurality of openings each of which is annular in shape, the pluralityof openings are concentrically arranged, an exposed part of thesemiconductor layer exposed from the second opening part includes: afirst region where the first electrode is provided on the exposed part;and a second region where the first electrode is not provided on theexposed part, and the first region and the second region are locatedalternately in a radial direction.
 20. A semiconductor light receivingelement, comprising: a substrate; a semiconductor layer of a directtransition type on the substrate, the semiconductor layer havingsemi-insulating properties; a p-type semiconductor layer on at leastpart of the semiconductor layer; a first electrode electricallyconnected to the semiconductor layer and in contact with the p-typesemiconductor layer; and a second electrode spaced apart from the firstelectrode and at least partially in contact with one of thesemiconductor layer and the substrate, wherein the first electrodeincludes a first opening part, the second electrode is provided on abottom surface of the substrate, the semiconductor layer includes aportion where an impurity concentration in a stacking directioncontinuously changes, and the impurity concentration of the portion ishigher in an uppermost region than in any other region.